High speed and high power light sources, particularly lasers and light-emitting diodes (LEDs) are used in numerous industrial, biomedical and defense applications. Many laser-based material processing e.g., laser drilling, cutting, engraving welding etc., require pulses of high speed and power. Likewise, LEDs become ever more popular as light source for microscopy and machine vision systems, requiring bright and often strobed (pulsed) illumination. Other applications, particularly those involving diode lasers, or fiber lasers require arbitrary waveform shape, where the waveform is specified point-by-point by the user. The shape of the waveform namely, the amplitude, pulse duration, the rise time and fall, and other are essential part of the application. And while the shape of the waveform can be digitally defined with high precision, the actual optical output may differ from the specified waveform shape if the driver is not designed to match the specific characteristics of the light source.
U.S. Pat. No. 7,348,516 to Sun et al. describes three different laser architectures providing a certain control over the laser pulse shapes. U.S. Pat. No. 6,281,471 to Smart, entitled “Energy-efficient, laser-based method and system for processing target material” describes many requirements and specifications concerning the temporal generation of square laser pulse shapes in material processing. The system presented therein includes, among its main components, a controller for generating a processing control signal, and a signal generator for generating a modulated drive waveform based on the processing control signal. A common pulse shaping technique such as for example disclosed in U.S. Pat. No. 7,428,253 issued to Murison et al. uses digital electronic means where sequence of digital points stored in a memory is passed to a digital-to-analog converter (DAC). The shaped analog signal output by the DAC is then fed to a an amplifier having enough bandwidth and drive capability for directly modulating a light source such as a laser diode U.S. Pat. No. 8,073,027 to Deladurantaye et al describes a practical architecture for implanting digital pulse shaping module for controlling a pulsed laser oscillator.
Although the aforementioned inventions provide solutions for shaping an optical waveform, they do not address directly the difficulties associated with certain physical characteristics of light sources and matching the current waveform to the light output thereof.
One such difficulty associated with driving a light source such as a laser diode (LD) and LED is a time delay between an on-off transition in the drive current and the on-off transition in the light output. This time delay results from a relatively large capacitance and inductivity of a typical LD or LED. A common approach in the art to address the issue is by pre-shaping the electrical pulses that drive the light source. For example, U.S. Pat. No. 4,818,896, issued to Cavanna, discloses a driver which pre-shapes current pulses by adding current “spikes” during the rise and the fall of the light source in order to quickly charge and discharge the associated capacitances of the LED. Different architectures for realizing “peaking of leading and trailing edges of current pulses are disclosed in U.S. Pat. No. 5,343,323 (Lynn, et al) U.S. Pat. No. 5,115,147 (Kusano, et al), and U.S. Pat. No. 6,724,376 (Sakura, et al), U.S. Pat. No. 6,049,175 (Forsberg). U.S. Pat. No. 7,453,306 issued to Baumgartner discloses a driver for controlling both the height and the width of peaking current to account for variations in capacitance and inductance of LD and LED.
Another difficulty is to overdrive LDs and LEDs for having increased optical peak power but without scarifying their reliability.
While the above-mentioned generators provide solution for pulsed light sources, they do not address the situations where the laser or LED is required to operate at arbitrary waveform. Therefore, there is a need for an optical waveform generator that will provide the means for pre-shaping the driving waveform to comply with different lasers and LED providing various pre-programmed optical waveforms, and providing a multiple feedback options to adjust the pre-shaped waveform to the optical output thereof.